People almost never leave a backyard because the seating ran out. They leave because it got dark, or cold underfoot, or the bugs found them, or the neighbor's kitchen window was right there.
Every one of those has a fix that costs less than a chair.
1. Light you can sit under, not light that points at you
A floodlight over the back door ends an evening. It flattens everything, throws hard shadows, and makes the yard past it look like a wall of black. What keeps people out is low, warm light scattered at knee and table height, the kind you read as glow rather than illumination.
Solar stake lights are the easiest version of this because there is no wiring decision to regret. Push them into the border where people walk, not into the middle of the lawn. You want the edges of the space lit so the middle feels like a room.
2. Something under your feet
Bare concrete and decking radiate heat away fast. The moment the sun goes, the floor goes cold, and people put their shoes back on, which is the last step before going in.
An outdoor rug fixes it for about the price of two cushions. Look for a flat weave in polypropylene rather than natural fibre: it will not hold water, it rinses with a hose, and it can stay out through a rain shower without going sour. Size it so the front legs of every seat land on the rug. A rug that only covers the middle of the space makes the space read smaller, not larger.
3. A wall on one side
Nobody relaxes in the open. This is not a design theory, it is just how people sit, check any restaurant patio and the edge tables fill first. If your yard or balcony has no side to put your back to, build one: a screen, a hedge panel, a run of greenery along the railing.
It does not have to enclose the whole space. One solid side is enough to turn an exposed rectangle into somewhere you would sit for two hours.
4. The door stays open
The single biggest thing that separates a yard people use from a yard people look at is whether the door between them is open. Closed door: the outside is a destination you have to decide to visit. Open door: it is another room.
The reason the door gets closed is almost always insects. A magnetic screen solves it and costs less than dinner, and unlike a fitted screen door it goes up in an afternoon and comes down in autumn.
The order to do it in
If you are doing one thing this month, do the light. It changes the hour you go inside more than anything else on this list, and it is the cheapest. Footing second, screen third, wall last, the wall is the one worth waiting to get right.